1. Field of the Invention
The present invention relates to a silent chain used as a power transmitting means such as a timing chain for an engine.
2. Description of the Related Art
A conventional silent chain known from Japanese Patent Laid-open Publication No. HEI 9-196126 includes, as shown here in FIG. 8, guide link rows A each having two guide plates A1 and three guide link plates A2 disposed the guide plates A1, articular link rows B each having four articular link plates B1 interleaved with the five plates A1, A2 in an adjacent guide link row B, and connecting pins C inserted through respective pin holes of the guide plates A1, guide link plates A2 and articular link plates B1 to articulately connect together the guide link rows and the articular link rows in an alternate fashion along the length of the chain, each of the connecting pins being press-fit at opposite ends with the pin holes of the laterally aligned guide plates A1.
For convenience of manufacture and control of parts of the silent chain, both the plates A1, A2 in guide link rows B and the plates B1 in articular link rows A are designed to have a uniform thickness.
From the structural point of view, the number of plates A1, A2 disposed in each guide link row A and the number of plates B1 disposed in each articular link row B necessarily differ from each other. This difference causes a problem that due to an unbalanced tensile strength in the longitudinal direction of the chain about each connecting pin, the link plates B1 in each articular link row B having fewer links than the guide link row A form a weak point in terms of the chain strength.
Furthermore, as shown in FIG. 9, since the opposite ends of the connecting pins C are fixed by press-fitting to the pin holes of the guide plates A1, a chain tension produced during power transmitting operation of the chain causes the connecting pins C to flex or bend as indicated by the arrowheads. Especially, two outer ones of the articular link plates B1 located adjacent to the guide plates A1 suffers from uneven contact with the connecting pin C due to concentration of a tensile load, producing an excessively large surface pressure acting on the circumferential surfaces of the pin holes of these outer articular link plates B1. This may cause undue wear of the pin hole circumferential surfaces, resulting in the occurrence of a wear elongation of the chain. As the wear elongation increases, the two outer articular link plates B1 are most likely to become ruptured. This may cause rupture of the silent chain as a whole.
The press-fit connection between the connecting pin C and the guide plates A1 in each guide link row A prevents rotation of the connecting pin C relative to the plates A1, A2 of the guide link row A and allows rotation of the connecting pin C relative to the link plates B1 of the adjacent articular link row B. This arrangement leads to formation of circumferential grooves on the outer surface of the connecting pin caused due to abrasion with the articular link plates B1. The connecting pin C is susceptible to breakage at the grooved portions during a relatively short period of use, which may cause rupture of the silent chain.
With the foregoing problems in view, an object of the present invention is to provide a wear-elongation resistant silent chain which can prevent wear elongation of the chain from occurring during power transmitting operation of the chain and also prevent rupture of the link plates in articular link rows and breakage of the connecting pins.
To achieve the foregoing object, according to the present invention, there is provided a wear-elongation resistant silent chain comprising: guide link rows each having a pair of guide plates and at least one guide link plate disposed between the guide plates; articular link rows each having at least two articular link plates interlaced with the guide link plate of the adjacent guide link row, the number of the articular link plates in each articular link row being one more than the number of the guide link in each guide link row; connecting pins inserted through respective pin holes of the guide plates, guide link plate and articular link plates so as to articulately join the guide link rows and the articular link rows in an alternate fashion along the length of the silent chain; and guide plate retainers each secured to one of opposite ends of each of the connecting pins to keep the guide plates in position against removal from the connecting pins. The guide link plate and the articular link plates have different thicknesses so dimensioned as to balance the tensile strength of the guide link plate in one of the guide link row and the tensile strength of the articular link plates in the adjacent articular link row that are connected by one of the connecting pins.
The guide plates may take any configurations provided that they have a pin hole loosely receptive of the connecting pin. For example, a guide plate having a pair of pin holes larger in diameter than pin holes formed in guide and articular link plates, a guide plate having an opening formed between two pin holes so as to reduce the weight of the guide plate, or a guide plate having a single oblong aperture corresponding in length to the outside distance between a pair of pin holes of a similar guide plate can be used.
The guide plate retainers may take any forms provided that they can prevent removal of the guide plates from the connecting pin while permitting articulate movement of the guide plates, guide link plates and articular link plates relative to the connector pin. Examples of the guide plates include a press-fit washer adapted to be press-fit on the connecting pin, a split cotter pin adapted to be inserted in a hole to hold the guide plate to the connecting pin, and a stopper plate adapted to be attached by caulking to the connecting pin. From the viewpoint of downsizing, weight-reduction, structural simplification, manufacturing cost and maintenance, the press-fit washer is preferable.
The number of the guide link plates is preferably three or greater because this arrangement can increase the degree of design freedom to such an extent that a tendency for bending of the connecting pins to occur is prohibited with increased efficiency by differentiating the thickness of the guide link plates and the thickness of the articular link plates.
In the wear-elongation resistant silent chain of the present invention, since the guide link rows and the articular link rows are articulately connected together in an alternate fashion by means of the connecting pins inserted through respective pin holes in the guide plates, guide link plates and articular link plates, a chain tension acting around each individual connecting pin during power transmitting operation of the silent chain is borne by the guide link plate of one guide link row and the articular link plates of the adjacent articular link row without exerting any influence on the guide plates that are mounted by sliding fit on the connecting pin. At the same time, the guide plates, guide link plate and articular link plates contact uniformly with the circumferential surface of the connecting pin.
The guide plate retainers secured to the opposite ends of each connecting pin keep the guide plates in position against removal from the connecting pin without restraining mutual movement of the adjacent connecting pins. The guide plates are, therefore, freed from the tensile load applied during power transmitting operation of the silent chain.
In the wear-elongation resistant silent chain of the present invention, since bending of the connecting pins is suppressed by differentiating the thickness of the guide link plates and the thickness of the articular link plates, the tensile strength of the guide link plate in one guide link row can balance the tensile strength of the articular link plates in the adjacent articular link row regardless of the difference in number of the link plates. Thus, the guide link plate and each of the articular link plates can engage the connecting pin uniformly at a constant surface pressure. This ensures that chordal oscillation of the chain, which may occur due to wear elongation of the chain, is prevented from occurring over a long period of time, and stable power transmitting operation of the silent chain can be maintained.